What makes you think there is a cold spot, KTpekin? I have one of these incis and there is no possibility of a gap where the top fits on to the base, so I'm sure it's not that. There is sometimes a bit of condensation on the plastic dome, but I only noticed this when the humidity was raised at pipping, so I wonder what humidity you are setting for it? Mine doesn't have a built-in hygrometer, though I think the newer ones do. I just incubated dry until the eggs pipped and then added water to the pots when turning ceased and I opened it to fit the nonslip matting over the floor. I had two excellent hatches, with all the fertile eggs emerging easily.
Have you tried placing two thermometers at different places inside? They would have to be the same kind of thermometers as otherwise you couldn't rely on their readings being exactly the same. As the eggs get gradually rotated when the incubator turns them, presumably any difference would be fairly unlikely. I wonder where you have the incubator - could it possibly be in a draught, somewhere where one side gets cooler (or hotter) than the other? Otherwise, if you are convinced that one egg is behind the others, and that it is in a cooler area, why not move it to what you think might be a warmer place? Or just turn the incubator round a bit to even out any environmental factors?
This is a very small incubator and I would hesitate to insulate it in any way as I think this would affect the fan ventilation. Also,they are well-known for being very reliable and easy to use for small numbers of eggs, so if there are any problems with the way it works at least it's under guarantee from Brinsea.
